Preliminary analysis of the GABA-induced current in cultured CNS neurons of the cutworm moth, Spodoptera litura

Properties of GABA-induced current in cultured CNS (ganglion) neurons of cutworm moths (Spodoptera litura) were studied using a whole-cell patch-clamp technique. CNS neurons ranging from 10 to 20 μm in diameter were cultured for 4-7 days in MGM-464 medium. GABA-induced a current response in these neurons in a sigmoidally dose dependent manner where the Hill coefficient and EC50 were 2.2 and 33.0 μM, respectively. The reversal potential of GABA-induced current was −2.5 mV, which is close to the Cl− equilibrium potential that was calculated from chloride ion concentrations in the present experimental environment. Furthermore, the GABA-induced current response depended on the extracellular chloride ion concentration, indicating that the receptor regulates the Cl− permeability of cells. The GABA-induced current was completely inhibited by the GABAA antagonist, SR95531, and activated by the GABAA agonist, muscimol but not by the GABAB agonist, baclofen. On the other hand, the GABAC agonist, CACA, also induced a little smaller current than the GABA-induced response. The pharmacological behaviors of the GABA-induced currents suggest that these cells contain GABA receptors that belong to the GABA receptor family including the Rdl GABA receptors identified in Drosophila neurons.